In imaging devices, e.g., cameras, there is often a need for a large depth of field. Depth of field is the portion of an image which is “in focus” on either side of an in focus focal point in the image. Objects outside of the depth of field will appear blurry.
Referring to FIG. 1, a digital imager 100, e.g., a digital camera, having a conventional fixed focus lens system is shown in a cross-sectional view. The imager 100 includes a sensor module 170, formed over a substrate 180, which comprises an image sensor 150 having a pixel array and being formed over an attachment layer 160. FIG. 1 schematically shows a fixed focus lens 130 mounted in lens mount 120 in a fixed position over module 170. Incoming light 110 is focused by fixed focus lens 130 onto image sensor 150.
The conventional fixed focus lens 130, shown in FIG. 1, has a fixed position relative to sensor module 170 and is designed such that objects which are at a predetermined distance in front of the lens are in focus. There is a fixed focal length (f0) from lens 130 to focal point 140, where f0 is the distance from L1 to L2, which correspond to the positions of lens 130 and focal point 140. There is a limit on the distance from the lens 130 (or focal point 140) at which objects are in focus. For example, objects that are either nearer or farther from a predetermined in-focus distance from the lens 130 will not be in focus.
Referring to FIG. 2, a conventional manually or automatically focus adjustable lens digital imager system 200, e.g., a digital camera, is shown in a cross-sectional view. The system 200 includes an adjustable focus lens 230 and a sensor module 270 formed over substrate 280. The system 200 additionally includes image sensor 250 having a pixel array formed over an attachment layer 260. Incoming light 210 is focused by lens 230 into the image sensor 250. Adjusting the position of the lens relative to the image sensor 250, changes the in focus distance from an object in an image to lens 230. Thus, the focal length f1 may be changed when lens 230 is adjusted to bring a desired object within an image into focus. However, whatever focal position is used to focus on an object, there is still a limited depth of field associated with the focus position.
In sophisticated cameras having a variable aperture, depth of field can be increased somewhat by using smaller aperatures which pass lens light. This reduces the brightness of the overall image seen by a sensor and also requires longer image capture times.
In many instances, it would be desirable to increase the depth of field without aperture adjustments, or other complicated procedures.